A lot of people are interested in using red focus lights, since underwater subjects apparently tolerate it better than white light. Is there any evidence that fish respond less to some wavelengths of visible light? Focusing with red light reduces the intensity of the light directed at the subject, so is it the lower intensity, rather than the colour, of a red focus light that keeps the critters calm?

If the colour red is less visible or less alarming to fish, how important do you think it is that a particular shade of red be used? Is it likely that using any reddish transparent or translucent filter over a cheap dive light would serve the purpose as well as an expensive dive light equipped with red LEDs?

Are marine animals so different from one another that it it is impossible to make generalizations about how and why they react to light? What about creatures that live a particular depth range - do they usually share a similar response to light?

I had a quick look through some of the scientific literature and it appears that many/most fish can see red light. But at least for deeper water fish they may never have seen red and therefore not learned to associate anything red with danger. The proof is in the pudding though. If people generally observe a positive difference then it apparently works.

FWIW, I was using a green underwater laser pointer on my visit to Roatan, and accidentally discovered that many (but not all) fish seem to respond to, and will chase, the green light spot, especially on white sand. It is actually rather amusing, similar to exercising a cat with a laser pointer. Goatfish, among others, seem to really go nuts chasing the light spot.

FWIW, I was using a green underwater laser pointer on my visit to Roatan, and accidentally discovered that many (but not all) fish seem to respond to, and will chase, the green light spot, especially on white sand. It is actually rather amusing, similar to exercising a cat with a laser pointer. Goatfish, among others, seem to really go nuts chasing the light spot.

I donīt know about fish because I try to avoid taking pictures of them at night, but many crustaceans donīt even notice you when approaching them during a night dive with a red light (whereas doing the same with a white light would scare them fast). I use an old fantasea with a red plastic and it is good enough.

FWIW, I was using a green underwater laser pointer on my visit to Roatan, and accidentally discovered that many (but not all) fish seem to respond to, and will chase, the green light spot, especially on white sand. It is actually rather amusing, similar to exercising a cat with a laser pointer. Goatfish, among others, seem to really go nuts chasing the light spot.

Sure do - this is the one that I got, and it worked quite well, although I have only used it on this one dive trip so far, so I have no information on long term reliability. It does appear fairly well made, though.

Hi Alex, I actually discovered it by accident. I was pointing out a tiny flounder to my dive partner, when the flounder was attacked by a school of goatfish who just went nuts. Then I started playing with the pointer and they followed it. It amused me for the rest of the trip, off and on. I wonder what the flounder thought when the goatfish jumped all over it?

Interesting issue. I've seen the low reaction to a red light that most crustaceans have, or rather the lack of reaction. My guess would be it is actually due to their ability to see a much wider spectrum than us, so that red light ends up being a very low level of light.

Gulf flounder appear to have color vision very close to humans, as their red color match capabilities decreases about the same as we do and they are terrible an depths below 60 feet.

Fire worms and Spotted scorpion fish can accurately red color match to well over 33 meters in 5 meter vis water. Well past the point where we can see any red. My guess is a red light would effectively blind them.

Note: Not actually sure how a fire worm, that does not actually have eyes can "see" color, but they do.

Note 2: Have also seen them color match reds at night... so they most be really, really sensitive, as well as over 44 meters deep

So my guess is that red light blinds some animals, is not seen by some, and is not well seen by others

Interesting issue. I've seen the low reaction to a red light that most crustaceans have, or rather the lack of reaction. My guess would be it is actually due to their ability to see a much wider spectrum than us, so that red light ends up being a very low level of light.

Gulf flounder appear to have color vision very close to humans, as their red color match capabilities decreases about the same as we do and they are terrible an depths below 60 feet.

Fire worms and Spotted scorpion fish can accurately red color match to well over 33 meters in 5 meter vis water. Well past the point where we can see any red. My guess is a red light would effectively blind them.

Note: Not actually sure how a fire worm, that does not actually have eyes can "see" color, but they do.

Note 2: Have also seen them color match reds at night... so they most be really, really sensitive, as well as over 44 meters deep

So my guess is that red light blinds some animals, is not seen by some, and is not well seen by others

Hello Puffer Fish,

It seems that marine animals have a varied response to light, and David Barrio has had good luck with red plastic over an inexpensive focus light. That's all good news for someone like me who has hit the wall on spending.

I'm pretty skeptical that it requires pure red light from an LED to avoid disturbing underwater subjects. Is there any evidence to suggest that a very specific wavelength is important in this regard? A homemade red plastic diffuser produces a wide beam of soft red light. Is it not possible that such a light may impact even less on a creature's eyes than more powerful LED lights. I won't be able to make the comparison because I'll just have to get by with the light I presently own (it has already been noted that I have lost the run of myself over this camera).

I see there is also a, less powerful, red underwater laser (only $24). Playing with that may help figure out whether a fish is blind to red light (hopefully without blinding him in the process), or just less averse to it.

It seems that marine animals have a varied response to light, and David Barrio has had good luck with red plastic over an inexpensive focus light. That's all good news for someone like me who has hit the wall on spending.

I'm pretty skeptical that it requires pure red light from an LED to avoid disturbing underwater subjects. Is there any evidence to suggest that a very specific wavelength is important in this regard? A homemade red plastic diffuser produces a wide beam of soft red light. Is it not possible that such a light may impact even less on a creature's eyes than more powerful LED lights. I won't be able to make the comparison because I'll just have to get by with the light I presently own (it has already been noted that I have lost the run of myself over this camera).

I see there is also a, less powerful, red underwater laser (only $24). Playing with that may help figure out whether a fish is blind to red light (hopefully without blinding him in the process), or just less averse to it.

John McCracken

John, All the spectral data I have seen on organic light sensitive compounds shows them to be sensitive over some fairly wide spectrum, so I think it would be safe to say that it would not be a single or very narrow frequency

But they do have eyes. It's just that the eyes aren't easily seen in the large amphinomid species with prominent caruncles overlying the head.

Not all amphinomidae polychaetes have "eyes", but you are correct. However, their "eyes" would hardly be considered highly developed. I was referring to eyes in the sense of highly developed, wide spectrum, focusing sensing organs. Clearly they (well, except for the ones that don't have any eyes) have a far better color vision than we humans.

As they tend to be night feeders, and can live fairly deep, it would seem (at least to me) rather odd to be extremely sensitive to red light. The other obvious option would be that they have a highly complex multi-frequency photo-sensitive compounds...which would be really interesting if they do.

Also those eyes are located in a rather shaded, dark location, not the best for seeing anything, particularly for a night animal

I also notice there is some belief that some may have light sensing organs on their top side.

Green lasers do indeed make fish crazy. Jacks really like them a lot and if you get the Jacks worked up Reef Sharks will soon appear to see what all the hub-bub is about. I had a red U/W laser for awhile, but the fish pretty much ignored it.

One concern (and probably a pretty major one) I have about the use of red focusing lights is the contrast to strobes. If the organisms truly are less sensitive to the red light (and it appears not all are) then they won't "see" the focus light and won't react to it. How much worse, then, are the strobes firing? Sure, you're more likely to get your shot, but what is the impact on the organism?

Now, if you're using a white focusing light, at least the difference between the focusing light and the strobe will be less.